A line of bull means a lot of nonsense. Bull is quite a common word meaning specious nonsense. (see http://dictionary.cambridge.org/define.asp?dict=CALD&key=10159)"They're feeding the people a line of bull, and they are spinning and people are dying," a New Orleans Major said.
This is an old puzzle for me.
a promise, a pledge?
What is the connection to a bull, or to series of bulls?
I suspect that bullshit is a more common sight in the English-speaking world than zebrashit or octopusshit, but there may be other reasons.Thank you Thomas. But why bull instead of zebra or octopus?
I don"t feel the link between nonsense and bull. However I now understand the sentence.